1. Field of the Invention
The present invention relates to a method for controlling an apparatus which processes work pieces supplied intermittently and waits for the next processing during intervals between processings.
2. Description of Prior Art
An apparatus for processing work pieces supplied intermittently is so controlled, from the point of view of energy saving, that it operates at reduced energy levels in intervals between work pieces. FIG. 1 shows a system for controlling a rolling mill in the hot rolling line in such a manner that it operates at high energy levels only when a work piece is being rolled by the mill. Such system is disclosed in the Japanese Published Patent Application No. 55-147409. The continuous hot rolling line shown in FIG. 1 provides a rolling mill 7 consisting of a pair of rolls and this rolling mill serves for hot rolling of a work piece in accordance with well known procedures. Numeral 8 represents a preceding work piece which has already been processed as it passed through the rolling mill 7 and numeral 9 denotes a work piece which is newly supplied to the line for the hot rolling. The period between the supplying of a successive work piece 9 to the line and the supplying of the preceding work piece 8 to the line is defined as a supply pitch or an interval between processings and this interval can be adjusted.
A motor 6 for driving the rolling mill 7 receives power from a power supply (not shown) through a main switch 1 and a power converter 4. The motor 6 includes a field winding 6a and such winding is connected to the power supply through the switch 2 and the power converter 5. A cooling fan motor 12 connected to the power supply through the switch 3 is provided for cooling the motor 6.
The controller shown at reference numeral 10 controls the power converter 5 in accordance with the heading end and trailing end detection signal 11 of each work piece supplied from the rolling mill 7 so that the output of motor 6 is kept at the predetermined increased value during the rolling process of the work piece. The controller 10 also controls the power converters 4 and 5 during the period from the time when the preceding work piece 8 exits from the rolling mill 7 to the time when a successive work piece 9 arrives, so that the output of the motor 6 is suppressed either by decreasing the main circuit voltage 6b or by keeping the field current of the field winding 6a to a reduced value. While the output of the motor 6 is kept at this low level, power consumption of motor 6 is reduced as compared with continuous operation of the motor at its maximum output, and thus energy can be saved by this reduction of power consumption.
A problem of the conventional control described above is that the machine indicated as the rolling mill 7 in the example of FIG. 1 must always be kept at the reduced operating condition awaiting the arrival of the successive work piece during the interval between work pieces, and energy required for such waiting condition is consumed uselessly.